Anomalous X-ray scattering studies on glassy GexSe1-x across the stiffness threshold composition x=0.20

Anomalous x-ray scattering experiments on glassy GexSe1-x have been carried out at energies close to the Ge and Se K edges at concentrations close to tire onset- and at the mid-point of the rigidity percolation threshold (x = 0.195 and 0.23). The total structure factors S(Q) show rapid variations in both the position and intensity of the prepeak around 11 nm(-1), while it stays almost unchanged in the remaining Q range, The differential structure factors Delta(1)S(Q) comprise characteristic features. Comparing them suggests that the prepeak purely originates from the Ge-Ge correlation. The present structural results strongly support the chemically-ordered continuous-random-network model for the Ge-Se glasses. The origin of the prepeak was discussed from a comparison between the S-GeGe (Q) of g-GeSe2 obtained by Petri et al. and S(Q) of a-Ge. The concentration dependence of the prepeak is consistent with the Raman data, which reveal the diminishing. of short Se chain connections between the Ge(Se-1/2)(4) tetrahedra near the stiffness transition composition.